The present invention relates to radio telecommunication systems. More particularly, and not by way of limitation, the present invention is directed to a method of measuring signal strengths of signals from neighboring cells in a cellular radio telecommunication system.
In a cellular radio telecommunication system such as the Global System for Mobile Communications (GSM), each active mobile station (MS) operating within the coverage area of a given cell measures the signal strength of the traffic channel on which the mobile station is operating, together with the signal strengths of the control channels of neighboring cells. These signal strength measurements are reported to the system, which uses them to make handover and reselection decisions. However, the measurements currently made by MSs in GSM networks lack accuracy, and therefore lead to less than optimum handovers and erroneous target cell identification.
A method to improve the accuracy of neighbor cell RSSI measurements has been suggested in a paper by S. Craig, C. Jansson, Y. Timner, and T. Tynderfeldt entitled, “Efficient Broadcast Frequency Utilization—A Key to High Capacity Cellular Networks”, VTC, Fall 2003 (“the Craig paper”). The Craig paper describes a method that uses channel estimation during neighbor cell measurements to isolate the signal strength of the neighbor cell, thereby improving the accuracy of the measurement. However, a problem with this method is that the neighbor cell measurement has to be done at a specific time, corresponding to when the training sequence of the neighbor cell occurs. In a synchronized system, the appropriate time can be easily determined to a fair degree of accuracy, but this is more difficult in an unsynchronized system. There may also be problems if the MS is operating in a high multislot mode (for example, DTM 3+2). A high multislot mode is a mode in which the MS receives and transmits multiple slots, thereby having less time to make an RSSI measurement on a neighboring cell. Thus, when operating in a high multislot mode, the switching requirements on the MS's synthesizer may preclude making the neighbor cell measurement on the training sequence without breaks in transmission or reception.